\(\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}{\dfrac{19}{1}+\dfrac{18}{2}+\dfrac{17}{3}+....+\dfrac{1}{19}}\)

\(=\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{4}+...+\dfrac{1}{20}}{1+\left(\dfrac{18}{2}+1\right)+\left(\dfrac{17}{3}+1\right)+\left(\dfrac{1}{19}+1\right)}\)

\(=\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{20}}{1+\dfrac{20}{2}+\dfrac{20}{3}+...+\dfrac{20}{19}}\)

\(=\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{20}}{20.\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{19}+\dfrac{1}{20}\right)}\)

\(=\dfrac{1}{20}\)

1)
a) \(34,2:36=0,95\)
b) \(36,18:18=2,01\)
c) \(5,05:25=0,202\)
d) \(17,25:75=0,23\)
2) 
a) \(75,52:32=2,36\)
b) \(4,68:13=0,36\)
c) \(81,6:34=2,4\)
d) \(134,4:42=3,2\)
3) 
a) \(882:36=24,5\)
b) \(78:24=3,25\)
c) \(3:15=0,2\)
d) \(15:75=0,2\)
4) 
a) \(3:75=0,04\)
b) \(750:300=2,5\)
c) \(390:12=32,5\)
d) \(54:24=2,25\)

bạn ơi bạn có thể đặt tính giúp mình đc ko ???

12 - 1 = 11     13 - 1 = 12     14 - 1 = 13

17 - 5 = 12     18 - 2 = 16     19 - 8 = 11

14 - 0 = 14     16 - 0 = 16     18 - 0 = 18

\(\frac{11}{19}+\frac{19}{18}+\frac{8}{19}-\frac{1}{18}+5,2\)

\(=\left(\frac{11}{19}+\frac{8}{19}\right)+\left(\frac{19}{18}-\frac{1}{18}\right)+5,2\)

 \(=1+1+5,2\)

\(=7,2\)

\(\frac{11}{19}+\frac{19}{18}+\frac{8}{19}-\frac{1}{18}+5,2\)

\(=\left(\frac{11}{19}+\frac{8}{19}\right)+\left(\frac{19}{18}-\frac{1}{18}\right)+5,2\)

\(=\frac{19}{19}+\frac{18}{18}+5,2\)

\(=1+1+5,2=7,2\)

\(\dfrac{18}{17}:9=\dfrac{18}{17}\times\dfrac{1}{9}=\dfrac{18}{153}=\dfrac{2}{17}\)

\(\dfrac{8}{5}-\dfrac{18}{27}=\dfrac{216}{135}-\dfrac{90}{135}=\dfrac{126}{135}=\dfrac{14}{15}\)

\(\dfrac{2}{7}+\dfrac{5}{9}=\dfrac{18}{63}+\dfrac{35}{63}=\dfrac{53}{63}\)

`18/17:9 = 18/17 xx 1/9 =  2/17 `

`8/5-18/27     = 216/135 - 90/135 = 126/135 = 14/15 `    

` 2/7+5/9 = 18/63 + 35/63 =53/63`

\(18\times32+43\times18+18\times26-18\)

\(=18\times\left(32+43+26-1\right)\)

\(=18\times100\)

\(=1800\)

18 * 32 + 43 * 18  + 18 * 26 - 18

= 18 * ( 32 + 43 + 26 - 1 )

= 18 * 100

= 1800

Có số số  hạng là :

                   ( 100 - 1 ) : 3 + 1 = 34 ( số )

Tổng là :

                ( 100 + 1  ) x 34 : 2 + 83 = 1800